1.6.5 Using speech to good effect
Speech output is a powerful way of communicating information. It has particular benefits for the visually impaired. For those whose eyesight is good, speaking lifts may seem a novelty, but they provide useful information and reassurance for the visually impaired. Some applications of the technology have less obvious benefits, such as supermarket checkouts that read out the product and prices. These were found to breach the customer's sense of privacy and to be noisy. Again, good design depends upon a good understanding of the users and the environment in which the technology is going to be used. Box 2 describes an interesting speech-based system, but how many customers would want their financial details broadcast to the high street?
One of the benefits of good-quality speech output over text is that it communicates tone of voice, pace and accent. In this way it provides more information and helps to make the speaker seem more real to the user. The tone of voice can differ according to the content of the message: a warning message could sound urgent and an information message could sound reassuring.
Box 2: Advanced automatic teller machines (ATMS)
Over more than 30 years, bank ATMs have transformed the way in which we carry out banking transactions. However, the basic interaction technology has remained unchanged, using a numeric keypad and some buttons arranged around a small monochrome screen. More recently, this has been augmented by sound output indicating when an action needs to be taken, such as removing the card from the machine.
This approach has worked very successfully, but there have been ongoing problems with security. In particular, stolen cards can be used in the machines if the PIN number is known. One way around this is the use of iris recognition. In such systems, the user is required to look into a camera. The camera then takes a photograph of the iris, the coloured area around the pupil, and analyses the complex patterns. These patterns are unique to an individual and hence allow the system to identify the user.
A system known as STELLA is being piloted by NCR in Canada. In addition to allowing for iris recognition, this also allows for speech recognition and generation. Thus, the user walks up to the machine and stands on a pressure sensitive mat that indicates her presence. Having carried out the iris recognition, the user speaks to the system and the system provides the information available. Thus there is no keypad or screen.
Michaelis and Wiggins (1982) suggest that speech output is most effective when the following conditions are met:
message is simple
message is short
message will not be referred to later
message deals with events in time
message requires an immediate response
visual channels are overloaded
environment is too brightly lit, too poorly lit, subject to severe vibration or otherwise unsuitable for transmission of visual information
user is free to roam around
These guidelines assume that the output is digitised human speech or playbacks of tape recordings.
(See Shneiderman, 1988)